Oregon Revised Statutes Mineral Resources § 523.470

In addition to the authority to issue general obligation bonds, the district, when authorized at any properly called election, shall have the power to sell and dispose of revenue bonds, and to pledge as security therefor all or any part of the unobligated net revenue of the district or system, to purchase, acquire, lay out, construct, reconstruct, extend, enlarge or improve a geothermal heating system, for the purpose of obtaining geothermal heating for the use of consumers, within or without the boundaries of the district. The revenue bonds shall be issued in the same manner and form as are general obligation bonds of the district, but they shall be payable, both as to principal and interest, from revenues only, as specified by this section. The revenue bond shall not be subject to the percentage limitation applicable to general obligation bonds and shall not be a lien upon any of the taxable property within the corporate limits of such district, but shall be payable solely from such part of the revenues of the district as remain after payment of obligations having a priority and of all expenses of operation and maintenance of the district, including any taxes levied against it. All revenue bonds shall contain a clause reciting that both the principal and interest are payable solely from operating revenues of the district remaining after paying such obligations and expenses.